RNAi: Too Much of a Good Thing?

Whereas overexpression studies can yield results that may not ultimately be borne out in vivo, "knocked out" genetic mutants of animals can often be directly used to address the physiological function of a particular protein. However, in some model organisms, the engineering of specific gene-deficient animals is problematic. RNA interference (RNAi) is gaining popularity as a method in developmental biology and in cell culture for "technically knocking out" specific gene expression. Oates etal. however, caution that injection of double-stranded RNA (dsRNA), for RNAi experiments in zebrafish, leads to nonspecific effects. The authors first observed that injection of dsRNA corresponding to the T-box transcription factor tbx16/spt abrogated not only the expression of genes known to be affected by tbx16/spt, but also blocked expression of genes known to be independent of tbx16/spt influence. Injection of bacterial lacZ dsRNA in zebrafish also blocked the expression of tbx16/spt -dependent and -independent genes. In blind experiments, the effects of tbx16/spt or lacZ dsRNA were indistinguishable, suggesting that RNAi methodology may not be suitable for studying zebrafish development.